Natural Killer T (NKT) cells are innate-like cells of the immune system, capable of swift activation and production of cytokines. NKT cells have been shown to respond during bacterial, viral and fungal infections, as well as playing roles in autoimmune disease; causing damage to lung tissue in sickle cell disease and in asthma; and in the detection and elimination of malignant cells. While specific transcription factors and signaling molecules have been shown to be important for early stage development of NKT cells, many of the factors required for their maturation, maintenance and activation in the periphery remain unknown. I recently showed that the transcription factor HEB is essential for NKT cell development and also showed that the transcriptional regulator Id2 controls survival of NKT cells in tissues such as lung and liver. This proposal will illuminate the role of E proteins and te Id proteins in differentiation of this important cell type. I will explore how NKT cells respond to acute versus chronic infection and the factors associated with their activation versus anergic silencing. I will examine how NKT cell activation during infection affects other adaptive immune cells, namely CD8+ T cells. To this end I propose the following aims. Aim 1: Examine the role of both Id2 and Id3 during NKT cell differentiation and in the homeostasis and activation of these cells. My current data suggest the transcriptional regulators Id2- and Id3- are reciprocally expressed during NKT cell differentiation and in mature NKT cells in peripheral tissues. I propose, using recently generated reporter lines for Id2 and Id3, as well as Id2 and Id3- deficient lines, to examine how these transcriptional regulators impact NKT cell maturation and activation. Aim 2: Understanding NKT cell response to acute and chronic infection. NKT cells produce prodigious quantities of cytokines upon activation, as well as exhibiting cytotoxic function. This activation burst is followed by an anergic phase in which cells undergo apoptosis or remain resistant to proliferation. It is not known whether this anergic phase occurs in NKT cells during chronic infection or indeed whether NKT cells retain activity due to continual antigen stimulation. Using LCMV as a model of acute and chronic infection, I will examine the NKT cell response to persistent antigen stimulation. Furthermore, using microarray gene-expression analysis, I propose to examine the molecular changes that occur in NKT cells as they transition through the unresponsive phase during infection. The results from these studies will be useful in understanding development of NKT cells in the thymus and peripheral tissues as well as the factors required for their activation in acute and chronic infection. Aim 3: Define how NKT cells affect CD8+ T cell effector and memory formation upon activation. While NKT cells produce numerous inflammatory cytokines when activated, how this affects CD8+ effector and memory T cell formation, which are exquisitely sensitive to the inflammatory environment during infection, is completely unknown. Using NKT cell-deficient mice and T cell receptor-transgenic mice, I will examine effector and memory CD8+ T cell formation and function in the absence of NKT cells during infection. These studies will help to define the importance of NKT cells in acute infection and will assess how these cells influence immunological memory, an essential component of the immune system, required for protection from subsequent infection. These studies will be important for future vaccine design and efficacy. Project Narrative: Natural Killer T cells are elie cells of the immune system armed with the ability to rapidly produce an array of cytokines upon activation, and as such are thought to bridge the gap between the innate and adaptive immune responses. The research proposed here will examine the factors necessary for Natural Killer T cell differentiation, homeostasis as well as for their activation in acute and chronic infection. Furthermore, this research will examine how Natural Killer T cells interact with and influence other cells of the immune system to provide protection from disease. Recent studies show an important role for these cells in autoimmunity, cancer and lung disease, and therefore study of how these cells are maintained in peripheral tissues and the factors required for their activation will be of value to both biology and medicine.